System and method for controlling bobbin rotation in a sewing machine

ABSTRACT

A sensing system for detecting motion of a bobbin used in a chain stitch type sewing machine using a needle on one side of a textile workpiece and a rotary bobbin positioned on an opposing side of the textile workpiece includes the bobbin being held in a bobbin case having a side panel forming an aperture. The rotary bobbin has a side surface with arcuate regions around a perimeter of the side surface. In addition, the sensing system includes the first and second optical sensors aligned to detect the presence of the first or second bobbin surface. The sensing system further includes a controller adapted to receive signals from the first and second optical sensors related to the presence of the first or second bobbin surface in the first or second regions and interpret the signals to provide the detecting motion of the bobbin.

TECHNICAL FIELD

This invention relates to a bobbin in a stitch-forming machine and particularly to a system for controlling the bobbin rotation in a sewing machine and providing a method of monitoring a sewing process in the sewing machine having the bobbin. The invention finds a particular application in validating that a sewing operation provides a secure stitch used for example for producing motor vehicle seat belt system components.

BACKGROUND

The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.

Generally, a bobbin on a sewing machine runs in an uncontrolled manner during the sewing process as thread (or yarn) is drawn from the thread spool stored within the bobbin. For example, a marking-off of the rotary movement takes place after the beginning of each sewing process, the time of the marking-off and the strength of the incipient rotary movement, and the acceleration of the bobbin depending, among other things, on the degree of thread filling of the bobbin, on the material of the thread, and on the wear of the mechanical elements in the area of the bobbin, to mention just a few of the possible influential factors. Thus, the movement of the bobbin cannot substantially be readily predicted.

A sewing machine for forming a conventional chain stitch or related stitch type generally has an upper thread and a lower thread. The sewing operation requires the interlinking of the upper thread being delivered through the needle and the lower thread being delivered from the bobbin. In the event that this interlinking fails to occur, the situation can arise that the upper thread is delivered through the entire sewing pattern without the lower thread. For example, the wound-on lower thread quantity, or the lower thread supply, is typically smaller by an order of magnitude in relation to the upper thread supply on the spool situated outside the machine housing, and therefore must be refilled or exchanged more often. In addition, during sewing operation, the lower thread spool is not visible from the outside, because it is situated inside the hook housing, which is located in the lower arm. Accordingly, the monitoring of the momentary lower thread supply and of the pulling off of the lower thread during the sewing process is difficult.

As described above, since any type of monitoring and control in the area of the lower thread poses a major technical challenge because of the very confined spatial proportion, various proposed solutions for monitoring and controlling the lower thread of the sewing machine are developed. For example, during sewing operation, an optical device can be used having a light-emitting diode and a photodetector which passes light through holes directed parallel to the axis of the rotation of the bobbin when the lower thread on the bobbin is largely used up. If the bobbin still is filled with thread, the photodetector does not receive a light signal. A second sensor detects the movements of the hook, so that it can be clearly recognized whether the thread supply has been used up or whether the hook is merely standing still.

Another challenge in monitoring bobbin operation is adaptation of sensing devices with existing widely used sewing machine and component designs. A significant advantage is implementation with such existing equipment while providing reliable monitoring of lower bobbin operation. By monitoring thread being withdrawn from the lower bobbin, a reliable indication of a completed stitch being formed is provided.

However, there is a need to improve the system and process of monitoring and controlling the bobbin in the sewing machine for detecting incorrect bobbin rotation, which is not readily accessible. One approach implements a single sensor to detect the bobbin changing state during the sewing process. However, this solution has a proven risk that if the bobbin stops rotating at a border position, it is possible for the machine vibration to cause a change of the state in the sensor indicating rotation of the bobbin which is not occurring, resulting in the acceptance of a part without the lower thread.

SUMMARY

The present disclosure relates to a sensing system for detecting motion of a bobbin used in a chain stitch type sewing machine apparatus of a type using a needle on one side of a textile workpiece and a rotary bobbin positioned on an opposing side of the textile workpiece, wherein the bobbin is held in a bobbin case having a side panel forming an aperture. The bobbin has a side surface with arcuate regions around a perimeter of the side surface forming a plurality of first surfaces having a first color or reflectivity and a plurality of second surfaces having a second color or reflectivity. The first and second surfaces are interleaved along arcuate radial regions with respect to an axis of rotation of the bobbin such that upon rotational movement of the bobbin, and the first and second surfaces are alternatively exposed through the aperture. The sensing system further includes a first optical sensor aligned to detect the presence of the first or second surface at a first region of the aperture, and a second optical sensor aligned to detect the presence of the first or second surface at a second region of the aperture. The first and second regions are separated at differing radial positions with respect to the axis of the rotation. In addition, in the sewing machine, a controller is adapted to receive signals from the first and second optical sensors related to the presence of the first or the second surface in the first or second regions and interpret the signals to provide the detecting motion of the bobbin.

In accordance with a further aspect of the present disclosure, the signals represent first and second discrete states, wherein one of the first and the second discrete states is related to the presence of the first surface at one of the first and second regions and the other of the first and the second discrete states is related to the presence of the second surface at one of the first and second regions.

In accordance with a further aspect of the present disclosure, the side surface having three of the first surfaces and three of the second surfaces with each of the first and second surfaces extends over an arcuate range of 60° with respect to the axis of rotation. The signals from the first and second optical sensors represent four potential combination codes of the first and the second discrete states. In addition, the combination codes for the first and the second discrete states change twelve times in a complete single rotation of the bobbin.

In accordance with a further aspect of the present disclosure, the textile workpiece is a motor vehicle seat belt or airbag component, and the sensing system is implemented to validate the integrity of a sewing process wherein proper rotation of the bobbin established by the sensing system signifies proper feeding of the a sewing thread by the bobbin.

The present disclosure utilizes the fact that when the bobbin thread is properly delivered to the sewing pattern, the bobbin rotates continuously during the sewing process. The use of the two sensors offset from each other in the axis of the rotation of the bobbin for four separate and distinct signals to the controller ensures the rotation of the bobbin and continuous delivery of the bottom (lower) thread to the sewing pattern.

In addition, the present disclosure utilizes existing machined holes in the bobbin case for minimizing the cost of the implementation, and uses any variety of optical or laser sensors connected to the controller. In addition, bobbin markings can be made in a durable and cost effective method utilizing an inexpensive laser marker. Bobbin markings can also be machined into the bobbin utilizing any available machining technique.

Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the disclosure may be well understood, there will now be described various forms thereof, given by way of example, reference being made to the accompanying drawings, in which:

FIG. 1 is a view of a sewing machine having a sensing system in accordance with an embodiment of the present invention;

FIG. 2 shows detailed view of the sewing machine having the sensing system of FIG. 1 ;

FIG. 3 shows a detailed view of the sensing system having a sensor device and a bobbin case including a rotary bobbin of FIG. 1 ;

FIG. 4 is a side view of the bobbin case having the rotary bobbin of FIG. 3 ;

FIG. 5 is a plan view of the side surface of the rotary bobbin of FIG. 3 ;

FIG. 6 shows a dimension of arcuate regions on the side surface of the rotary bobbin of FIG. 3 ;

FIGS. 7(A) through 7(D) show a process of detecting the presence of the first and second surfaces on the rotary bobbin of FIG. 5 ;

FIG. 8 shows a table having binary combination codes of the first and second discrete states of FIGS. 7(A) through 7(D);

FIG. 9(A) shows a plan view of a bobbin having the side surface as prior art, and FIG. 9(B) shows a side view of a bobbin case having the bobbin of FIG. 9(A) as prior art; and

FIG. 10(A) shows a plan view of a bobbin having the side surface as prior art, and FIG. 10(B) shows a side view of a bobbin case having the bobbin of FIG. 10(A) as prior art.

The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features.

FIG. 1 illustrates a traditional sewing machine 10 such as a chain stitch type sewing machine. The sewing machine 10 includes a base 12, an upper arm 14, a lower or free arm 16, and a machine housing or body (not shown) connecting to the three parts. In the upper arm 14, a needle bar 18 and a needle foot 20 are fastened. The needle bar 18 which can move up and down is mounted in known manner. The needle bar 18 is driven by an arm shaft (not shown) which is supported in the upper arm 14 and the arm shaft is driven via a pulling means such as a V-belt or a chain by a driving motor (not shown). The sewing machine 10 further includes a sewing table 24 on which a textile workpiece is placed during operation of the sewing machine 10. Generally, this type of the sewing machine 10 uses a needle 22 on one side of the textile workpiece and a bobbin case 102 including a rotary bobbin 104 positioned on an opposing side of the textile workpiece for stitching.

FIG. 2 shows a detailed view of a sensing system 100 for controlling the rotation of the bobbin 104 in the sewing machine 10. The sensing system 100 including the bobbin case 102 is generally located under the sewing table 24 of the sewing machine 10. The bobbin case 102 under the sewing table 24 is coupled to a drive shaft (not shown) in drive connection with the main shaft (not shown) of the sewing machine 10. In addition, the sensing system 100 further includes a sensor device 106 as shown in FIG. 2 . The sensor device 106 includes a pair of optical sensors 108 for detecting the color (reflectivity or other detectable feature) on a side surface 110 of the rotary bobbin 104 (see FIG. 3 ).

FIGS. 3 and 4 illustrate the sensing system 100 having the bobbin case 102 with the rotary bobbin 104 and the sensor device 106 with the pair of optical sensors 108. The rotary bobbin 104 is held and covered by the bobbin case 102, and the bobbin case 102 has a side panel 112 forming an aperture 114. For example, the aperture 114 is disposed in an upper portion of the bobbin case 102. As shown in FIG. 3 , the pair of optical sensors 108 located along with the aperture 114 of the bobbin case 102 include a first optical sensor 107 and a second optical sensor 109 each detecting the color on the side surface 110 of the rotary bobbin 104 through the aperture 114 on the side panel 112 of the bobbin case 102. A general digital sensor with integrated optics and triggering and evaluation electronics may be used as the sensor device 106 in a compact design. As mentioned previously, optical detectors may be implemented to detect some other feature of discrete areas of the side surface 110 of the rotary bobbin 104. For example, the reflectivity or the absorption of light incident on the surfaces can differentiate them and enable the system to distinguish between the discrete areas. Sensitivity to “color” is used here generally to indicate a variation in output between the areas as detected by the optical sensors 108 and is not limited to differences in human visually perceived colors of the surfaces based on specular reflection.

FIG. 5 shows a plan view of the outer side surface 110 of the rotary bobbin 104. As shown in FIG. 5 , the rotary bobbin 104 includes the side surface 110 with arcuate regions 116 around a perimeter of the side surface 110. The outer side surface 110 of the rotary bobbin 104 exhibits a plurality of first surfaces 118 having a first color 120 or reflectivity and a plurality of second surfaces 122 having a second color 124 or reflectivity. The first and second surfaces 118 and 122 are interleaved along the arcuate radial regions 116 with respect to an axis X of rotation of the rotary bobbin 104 such that upon rotational movement of the rotary bobbin 104, the first and second surfaces 118 and 122 are alternatively exposed through the aperture 114 of the side panel 112 on the bobbin case 102. In FIG. 5 , for example, the first color 120 is a dark color and the second color 124 is a light color. According to an exemplary form of the present disclosure, other colors may be arranged for each of the first surface 118 and the second surface 122, which are clearly distinguishable from each other. In addition, the first and second colors 120 and 124 on the side surface 110 of the rotary bobbin 104 are marked with a laser. The bobbin markings can be made in a durable and cost effective method utilizing an inexpensive laser marker. Also, the bobbin markings can be machined into the bobbin with any available machining technique.

Referring back to FIGS. 3 and 4 , the sensing system 100 of the present disclosure is illustrated. As described above, the sensor device 106 having the first optical sensor 107 and the second optical sensor 109 interacts with the rotary bobbin 104 having the first and second surfaces 118 and 122. As shown in FIGS. 3 and 4 , the first optical sensor 107 is aligned to detect the presence of the first or second bobbin surface 118 and 122 at a first region 126 of the aperture 114 on the side panel 112, and the second optical sensor 109 is aligned to detect the presence of the first or second bobbin surface at a second region 128 of the aperture 114 on the side panel 112. For example, in the present disclosure, each of the first and second optical sensors 107 and 109 is arranged at a same radius R from the axis X of the rotation of the rotary bobbin 104. In addition, the first and second optical sensors 107 and 109 are preferably located within a radial distance A of 30° from each other with respect to the axis X of the rotation of the rotary bobbin 104. Generally, each of the first and second optical sensors 107 and 109 may be located within the radial distance A, which is between 28° and 32°. In addition, the first region 126 and the second region 128 of the aperture 114 are separated at differing radial positions with respect to the axis X of the rotation of the rotary bobbin 104.

Referring to FIGS. 5 and 6 , as described above, the rotary bobbin 104 includes the first surface 118 and the second surface 122. Each of the first and second surfaces 118 and 122 has three arcuate regions 116 alternatively, and each arcuate region 116 of the first surface 118 and the second surface 122 on the side surface 110 of the rotary bobbin 104 offsets by 60°. As shown in FIGS. 5 and 6 , for example, the rotary bobbin 104 includes three arcuate regions 116 having the first surfaces 118 with the first color 120 and another three arcuate regions 116 having the second surface 122 with the second color. That is, the side surface 110 having three of the first surfaces 118 and three of the second surfaces 122 with each of the first and second surfaces 118 and 122 extends over the arcuate range of 60° with respect to the axis X of the rotation of the bobbin 104.

As shown in FIG. 6 , in addition, the rotary bobbin 104 has a single radial marking from the rotation axis X of the rotary bobbin 104 as the arcuate regions 116 and the single radial marking has a dimension on the side surface 112 of the rotary bobbin 104. For example, an inner diameter d of the arcuate region 116 may be between 15 cm and 18 cm, and preferably is in one embodiment about 16.50 cm and an outer diameter D of the arcuate region 116 may be between 25 cm and 30 cm, and is preferably in one embodiment about 28.90 cm. Accordingly, the first and second colors 120 and 124 are marked within the dimension of the arcuate region 116 on the side surface 110 of the rotary bobbin 104. According to other forms of the present disclosure, the dimension of the arcuate region 116 may be changed according to the size of the rotary bobbin 104 or the radial distance A of the optical sensors 108.

Referring to FIGS. 9(A), 9(B), 10(A) and 10(B), well-known sensing systems 200 and 300 are illustrated as prior art. Each of the sensing systems 200 and 300 has two sets of radial markings offset at a different radius from the axis X of the rotation of each rotary bobbin 204 and 304. As shown in FIGS. 9(A) and 9(B), the rotary bobbin 204 in the sensing system 200 includes two sets of the radial markings and each set of the radial markings on the side surface 210 of the rotary bobbin 204 offsets from each other by 90°. In FIGS. 9(A) and 9(B), furthermore, two optical sensors 207 and 209 are spaced by 180° from each other.

As shown in FIGS. 10(A) and 10(B), the rotary bobbin 304 in the sensing system 300 includes two sets of the radial markings and each set of the radial markings on the side surface 310 of the rotary bobbin 304 offsets from each other by 45°. In FIGS. 10(A) and 10(B), furthermore, two optical sensors 307 and 309 are spaced by 90° from each other. However, in both sensing systems 200 and 300, it is required to have a machining operation on the bobbin case for having another aperture so that it adds cost to the implementation. In addition, this can impact the robustness of the bobbin case depending on the location of the second aperture and potential to interfere with moving part of the bobbin case.

FIGS. 7(A) through 7(D) illustrate how the sewing machine 10 having the sensing system 100 of the present disclosure is operated. In FIG. 3 , the sewing machine 10 further includes a controller 26 in the sensing system 100, and the controller 26 communicates with the sensor device 106 and transmits the sensed information to a server (not shown) for providing the status of the rotary bobbin 104. In FIGS. 7(A) through 7(D), the controller 26 is configured to receive signals from the first and second optical sensors 107 and 109 related to the presence of the first or second surface 118 and 122 in the first or the second regions 126 and 128, and interpret the signals to provide the detecting motion of the rotary bobbin 104. In the present disclosure, the signals represent first and second discrete states. One of the first and second discrete states is related to the presence of the first surface 118 on the side surface 110 of the rotary bobbin 104 at one of the first and the second regions 126 and 128, and the other of the first and second discrete states is related to the presence of the second surface 122 at one of the first and the second regions 126 and 128.

As shown in FIGS. 7(A) through 7(D) and FIG. 8 , the first and second discrete states are indicated as “0” and “1”, respectively as binary codes in the controller 26. For example, when each of the optical sensors 107 and 109 is related to the presence of the first surface 118 with the first color 120 (dark color), the first discrete state is indicated as “0” as a binary code, and when each of the optical sensors 107 and 109 is related to the presence of the second surface 122 with the second color 124 (light color), the second discrete state is indicated as “1” as another binary code. Accordingly, in FIG. 8 , the controller 26 detects a sequence 32 having four different binary combination codes and the sequence 32 is repeated three times in a complete single rotation of the rotary bobbin 104, so that twelve changes of the binary combination codes in the complete single rotation of the rotary bobbin 104 occur.

In FIG. 7(A) and FIG. 8 , in the sequence 32 of the rotary bobbin 104, both first and second optical sensors 107 and 109 are related to the presence of the first surface 118, so that the first and second discrete states are indicated as (0, 0) as the first binary combination code. In FIG. 7(B) and FIG. 8 , the first optical sensor 107 is continuously related to the presence of the first surface 118 and the second optical sensor 109 is related to the presence of the second surface 122, so that the first and second discrete states are indicated as (0, 1) as the second binary combination code. In FIG. 7(C) and FIG. 8 the first optical sensor 107 is related to the presence of the second surface 122 and the second optical sensor 109 is continuously related to the presence of the second surface 122, so that the first and second discrete states are indicated as (1, 1) as the third binary combination code. In FIG. 7(D) and FIG. 8 , finally, the first optical sensor 107 is continuously related to the presence of the second surface 122 and the second optical sensor 109 is related to the presence of the first surface 118, so that the first and second discrete states are indicated as (1, 0) as the fourth binary combination code. As shown in FIG. 8 , accordingly, one sequence 32 having four different binary combination codes is completed. As described above, the sequence 32 is repeated three times in a complete single rotation of the rotary bobbin 104 so that it is possible to detect and monitor twelve changes of the binary combination codes in the complete single rotation of the rotary bobbin 104.

In the sewing machine 10 of the present disclosure, the sequence 32 of the binary combination codes verifies if the rotary bobbin 104 is rotating in the correct direction and/or rotation speed according to the number of stitches defined in specific sewing pattern in the sewing machine 10, so that the sequence 32 detected in the controller 26 ensures correct bobbin rotation and delivery of bottom thread to the sewing pattern. In the sensing system 100, furthermore, the controller 26 includes a processor 28 and a memory 30. The memory 30 stores all data of the rotation count with the sequence 32 for all stitches, and in the processor 28, each stitch is evaluated for making comparison between the current stitch data and the previous stitch data stored in the memory 30. Accordingly, the sequence 32 having the binary combination codes can be verified in the controller 26.

As described above, the controller 26 is monitoring and controlling the changes on the state of the sensed optical sensors 108 with the movement of the rotary bobbin 104. In the controller 26, two main routines including an “encoder_bobbin” for monitoring the rotational position of the rotary bobbin 104 and a “bobbin_rotation” for evaluating a bobbin rotation against its sewing pattern have been created. The purpose of the “encoder bobbin” routine is to count the change of the binary combination codes as indicated in the first and second optical sensors 107 and 109. As described above, in this routine, the sequence 32 of the binary combination codes has four different binary combination codes and is repeated three times in one complete turn of the rotary bobbin 104, so that twelve changes of the binary combination codes occur.

Also, the “bobbin_rotation” routine verifies if the rotary bobbin 104 is rotating in the correct direction and/or its rotation speed according with the number of the stitches defined in its specific sewing pattern. The “bobbin_rotation” routine saves the data of a “rotation_count” for all stitches in order to detect an incorrect bobbin rotation. After that, each stitch is evaluated making a comparison between the current stitch data and the previous stitch data. If the change of the binary combination codes is not detected then the controller 26 increments a counter named “Count_No_Turn” and if this counter overpasses maximum number defined as a predetermined value, the controller automatically will send a failure of “Not turn of rotary bobbin”.

In addition, if the change of the binary combination codes is detected, then the counter is set to 0 and starts again a new sequence. When the counter is set to 0, two conditions are evaluated to decide if the rotary bobbin 104 is an OK turning or an over turning. If the number of the binary combination code changes is less than a predetermined maximum-turn change, then the rotary bobbin 104 turns okay. If the number of the binary combination code changes is more than the predetermined maximum-turn change, then it fails such that the rotary bobbin 104 is overturning. For example, the predetermined maximum-turn change may be set as seven (7) times. Furthermore, If data decrement is observed, then the rotary bobbin 104 may turn backward (i.e., a reverse rotation).

As described above, when the bobbin thread is being properly delivered to the sewing pattern, the bobbin 104 rotates continuously during the sewing process. The use of the two sensors 108 offset from each other in the axis X of the rotation of the bobbin for four separate and distinct signals to the controller ensures the rotation of the bobbin 104 and continuously delivery of the bottom (lower) thread to the sewing pattern. In addition, the textile workpiece is a seat belt, an airbag component, or a car seat cloth in a motor vehicle, and the sensing system 100 of the present disclosure is implemented to validate the integrity of the sewing process wherein proper rotation of the bobbin 104 established by the sensing system 100 signifies proper feeding of a sewing thread by the bobbin 104.

While the above description constitutes the preferred embodiments of the present invention, it will be appreciated that the invention is susceptible to modification, variation and change without departing from the proper scope and fair meaning of the accompanying claims. 

What is claimed is:
 1. A sensing system for detecting motion of a bobbin used in a chain stitch type sewing machine apparatus of a type using a needle on one side of a textile workpiece and a rotary bobbin positioned on an opposing side of the textile workpiece, wherein the bobbin is held in a bobbin case having a side panel forming an aperture, comprising: the bobbin having a side surface with arcuate regions around a perimeter of the side surface, the side surface forming a plurality of first surfaces having a first color or reflectivity and a plurality of second surfaces having a second color or reflectivity, the first and second surfaces interleaved along arcuate radial regions with respect to an axis of rotation of the bobbin such that upon rotational movement of the bobbin, the first and second surfaces are alternatively exposed through the aperture; a first optical sensor aligned to detect the presence of the first or second surface at a first region of the aperture; a second optical sensor aligned to detect the presence of the first or second surface at a second region of the aperture, the first and second regions separated at differing radial positions with respect to the axis of rotation; and a controller adapted to receive signals from the first and second optical sensors related to the presence of the first or the second surface in the first or the second regions and interpret the signals to provide the detecting motion of the bobbin.
 2. The sensing system in accordance with claim 1, further comprising the signals represent first and second discrete states wherein one of the first and the second discrete states is related to the presence of the first surface at one of the first and second regions and the other of the first and the second discrete states is related to the presence of the second surface at one of the first and second regions.
 3. The sensing system in accordance with claim 2, further comprising the side surface having three of the first surfaces and three of the second surfaces with each of the first and second surfaces extends over an arcuate range of 60° with respect to the axis of rotation.
 4. The sensing system in accordance with claim 3, further comprising the signals from the first and second optical sensors represent four potential combination codes of the first and the second discrete states.
 5. The sensing system in accordance with claim 4, further comprising the combination codes for the first and the second discrete states change twelve times in a complete single rotation of the bobbin.
 6. The sensing system in accordance with claim 1, further comprising the textile workpiece is a motor vehicle seat belt or airbag component and the sensing system is implemented to validate the integrity of a sewing process wherein proper rotation of the bobbin established by the sensing system signifies proper feeding of a sewing thread by the bobbin.
 7. A method of validating the integrity of a sewing process by detecting motion of bobbin used in a chain stitch type sewing machine apparatus of a type using a needle on one side of a textile workpiece and a rotary bobbin positioned on an opposing side of the textile workpiece, and having a bobbin case for enclosing the bobbin having a side panel forming an aperture, the method comprising the steps of: providing the bobbin having a side surface with arcuate regions around a perimeter of the side surface, the side surface forming a plurality of first surfaces having a first color or reflectivity and a plurality of second surfaces having a second color or reflectivity; providing the first and second surfaces interleaved along arcuate radial regions with respect to an axis of rotation of the bobbin such that upon rotational movement of the bobbin, the first and second surfaces are alternatively exposed through the aperture; providing a first optical sensor and aligning the first optical sensor to detect the presence of the first or second surface at a first region of the aperture; providing a second optical sensor and aligning the second optical sensor to detect the presence of the first or second surface at a second region of the aperture, the first and second regions separated at differing radial positions with respect to the axis of rotation; receiving signals from the first and second optical sensors related to the presence of the first or the second surface in the first or the second regions; and processing and interpreting the signals to provide the detecting motion of the bobbin.
 8. The method in accordance with claim 7, further comprising the step of representing first and second discrete states as the signals wherein one of the first and the second discrete states is related to the presence of the first surface at one of the first and the second regions and the other of the first and second discrete states is related to the presence of the second surface at one of the first and second regions.
 9. The method in accordance with claim 8, further comprising the step of providing the side surface having three of the first surfaces and three of the second surfaces with each of the first and second surfaces extending over an arcuate range of 60° with respect to the axis of rotation.
 10. The method in accordance with claim 9, further comprising the signals from the first and second optical sensors represent four potential combination codes of the first and the second discrete states.
 11. The method in accordance with claim 10, further comprising the combination codes for the first and the second discrete states change twelve times in a complete single rotation of the bobbin.
 12. The method in accordance with claim 7, further comprising the steps of providing the textile workpiece in the form of a motor vehicle seat belt or airbag component, and a sensing system is implemented to validate the integrity of sewing processes wherein proper rotation of the bobbin established by the sensing system signifies proper feeding of a sewing thread by the bobbin. 